how do i pebble dash a wall

Hi all, i need some advise/guidance on how to mix motor for pebble dash.
I have a 9 foot high by 9 foot wide wall that has been damaged with the frost, I am going to take the loose off to the measurements above and need to know what ratio sand to cement i use and what kind of sand i use. I know there is 2 coats to be done, the first being the scratch coat - what ratio do i mix to do this coat and secondly what ratio do i mix for the top coat which has the little pebbles in.